The drilling/completion process typically leaves drilling fluid and/or debris in the wellbore that needs to be cleaned up in order to improve well completion performance and to avoid damage to equipment subsequently delivered into the wellbore. This debris includes drilling fluids, cement sheaths/chunks or metallic shavings from milling or squeezing operations.
The debris can also damage the formation as well as the hardware in the wellbore. In deviated wellbores the solids loosened up by scrapers or brushes could tend to lie on the bottom if sufficient fluid velocities are not developed in the removal process.
In the past, the removal operation involved the use of brushes or scrapers that are run to bottom. Thereafter, the well is put into circulation and the debris is directed to the annular space around the string that delivered the brush or scraping tool to the well bottom. Other, techniques involve the same procedure but also add filters and magnets in an effort to collect the debris in the cleaning tool as it is being churned up. In some cases, the technique above is enhanced with pulling the tools off bottom after circulating and then circulating again, followed by returning the tools to bottom and circulating, yet again. Other techniques combine the addition of chemicals to assist in loosening up the debris. The problem with the circulation technique is that the surface equipment would rarely have the capacity to maintain turbulent flow in the surrounding annulus. As a result, the circulation technique allowed most all of the debris to settle back down in the wellbore rather than being brought to the surface with the circulating fluid.
In the past, as illustrated in several patents, there have been a variety of tools and techniques used to remove debris. U.S. Pat. No. 2,782,860 shows the use of reverse circulation into a pickup tube held by a packer inside a tubular. Several devices involve pulling vacuum on the tubular to suck fluid and debris into it. Some examples are U.S. Pat. Nos. 3,775,805; 4,630,691; 5,269,384; 5,318,128; 3,958,651 and 5,033,545 (fluid jet creates a vacuum). U.S. Pat. No. 5,402,850 uses a seal and crossover to force fluid with debris into the annulus around the tubular string for the trip to the surface. Other techniques involve reverse flow into the tubing string, such as: U.S. Pat. No. 4,944,348 and 5,069,286. Also of interest are U.S. Pat. Nos. 5,562,159 and 5,718,289.
The present invention addresses this shortcoming in the prior art by allowing the use of reverse circulation or simple fluid displacement into the tubing to maintain high fluid velocities for solids removal to the surface. Connection and release from tubing as it is being run into and out of the wellbore has been made easy with the development of tools illustrated in U.S. Pat. Nos. 6,390,190 and 6,415,862. These tools, designed principally for running in tubulars, such as casing, into a wellbore and keeping them filled or allowing circulation through the casing string to get it unstuck, now are adapted to assist in the new wellbore cleanout process. The tools described in these patents are adapted to sealingly engage the tubing supporting an inverted cup seal or/and cleaning equipment so that the loosened debris could be forced to the surface as the cup seal or/and cleaning equipment are advanced downhole. Displacement and/or reverse circulation can be used to drive fluid laden with cuttings up the tubing to the surface. At the surface, the returning cuttings and debris-laden stream can be directed to separation equipment and back to the mud pits. In a further refinement, ports can be used just downhole from a cup seal that is mounted above the cleaning equipment. Displaced or reverse circulating fluid could enter the ports directly above the cleaning equipment and below the cup seal for the return trip through the tubing to the surface. These and other advantages of the present invention can be more readily appreciated by those skilled in the art from a review of the details of the preferred embodiment described below and from the claims.